Abstract: Through the regional geological survey in scale of 1∶250000,the lithologic assemblage,biota fossils,sedimentary environment and sedimentary basin attribute of the Dacaotan Formation have been essentially understood.The re-defined Dacaotan Formation is considered as a set of the variegated continental facies clastic rock stratum with the fuchsia feature,which unconformitely overlies on the Shujiaba Formation and underlies the Dazhuang Formation,and its geologic age is late Devonian.It is different from the marine facies dark clastic rock stratum clipped carbonate rock on it.At that time,tectonics background are extension,really not the foreland basin of the pressing surroundings.It also implies the tectonic attribute in the southern fringe of Ordos Basin during late Paleozoic Era.